Read Network Topology

ABSTRACT

A read network topology for a matrix output device with a number of outputs determined by cross-joining “m” rows and “n” columns comprises a basic filtering block replicated for all the outputs and separately assigned to each of the outputs; each filtering block contains two filtering circuits that have a common input connection to the assigned matrix output and that provide two separate symmetrical and filtered outputs; all the row outputs (i) from the same row “i” but from different columns are interconnected to an input of an amplifier linked to row “i”, and all the column outputs (j) from the same column “j” but from different rows are connected together to an input of an amplifier linked to column “j”, the complete topology appearing when “i” and “j” are expanded in the respective intervals thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to PCTApplication No. PCT/ES2016/070950, filed Dec. 30, 2016, which, in turn,claims priority to Spanish Application No. P201531953, filed Dec. 31,2015, the entire contents of each application is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention refers to a readout network topology for matrixoutput devices useful in different sectors, and especially in the fieldof nuclear medicine.

BACKGROUND OF THE INVENTION

The present invention relates to a readout system for a Matrix OutputDevice (MOD), that provides appropriate filtering of sensor output noiseand avoids signal mixing of the different sensor outputs preserving theuseful part of the signals in a way that it can be possible to reproducethe distribution of sensor output signals across the matrix, requiringsubstantially less amplifiers than other traditional readout systemsthat used to amplify every output channel.

Position Sensitive Photo-Multiplier Tubes (PSPMT) are well known MOD inthe art. These have a photosensitive matrix output that converts lightphotons into electrical currents. The main components of a PSPMT are aninput window, a photocathode, focusing electrodes, dynodes and an anode.The photocathode is used for converting incoming light (photons) intoelectrons. These photoelectrons, which are a product of thephotoelectric effect, are directed by the voltage of focusing electrodestowards dynode stages. The dynodes are used to multiply the electrons bythe process of secondary electron emission. Electron gains ranges from10³ to 10⁸ depending on the number of dynode stages and interdynodevoltages of the PSPMT. The main electrical difference between a notposition sensitive Photo-Multiplier Tube (PMT) and a PSPMT is that thislast one provides multiple outputs in matrix form, that are activatedemulating the same geometrical position of the impinging photon (Gammaor X-Ray) at the photocathode surface.

Each PSPMT matrix output has the behavior, of a charge source or acurrent source depending of the way the light reaches the detectorsurface.

In general the PSPMTs can be read and digitized at every matrix output,but this requires a high number of electronic channels to be processed.Often, an intermediate readout circuit is used to reduce the number ofelectronic channels to process [U.S. Pat. No. 6,747,263 (Popov)].Usually, after the readout circuit the signals are acquired, digitizedand a Center of Gravity (COG) algorithm is used to provide the planarcoordinates of the center of light distribution on the photocathode [S.Siegel et al “Simple Charge Division Readouts for Imaging ScintillatorArrays using a Multi-Channel PMT”, IEEE TNS, Vol 43, No 3, p. 1634,June, 1996], (Siegel).

Some advanced readout electronics are able to provide, not only thecenter of light distribution, but also information about the shape oflight distribution, permitting further analysis like Depth OfInteraction (DOI) determination [U.S. Pat. No. 7,476,864 (Christoph)].

In recent years a new type of light detector called Silicon PhotoMultiplier (SiPM) has appeared. These detectors have an internalmicroscopic matrix of photodiodes small enough to assume that these willmostly capture individual photons at each photodiode. When an individualphotodiode is reached by one or more photons it changes to its activatedstate, generating a fixed current independently of how many photonsactivate it. The SiPM adds all the similar photodiodes outputs providinga fast analog output proportional to the number of activatedphotodiodes, which corresponds approximately with the number of photonsimpinging the SiPM.

The SiPM output can be the anode or the cathode, depending of the devicebias polarity.

Novel SiPMs are becoming more used in several applications to accuratelydetect visible light, for instance, scintillation light, and someresearch groups and companies, as well as the SiPM manufacturers, beganto create devices containing large Arrays of SiPMs, that we call SiPMA,fixed in matrix configurations with a topology similar to the one of thePSPMTs, and often with similar dimensions, to take advantage of anypossible systems compatibility, creating an advantageous substitutivecomponent for the standard MODs, (the PSPMTs), with faster responseamong other benefits. As the PSPMTs are normally connected to theacquisition systems by means of readout circuits to reduce the requiredchannels, similar or equivalent circuits are required for the SiPMAs.

In the same sense of the PSPMT, the SiPMA matrix outputs have thebehavior of charge sources or a current sources, depending of the waythe light reaches the detector surface, so, in this specification wewill assume and represent the matrix outputs indistinctly as charge orcurrent sources.

It is important to note a relevant difference between PSPMTs and SiPMAs,regarding the intrinsic noise of their respective detection units, i.e.PSPMT individual output anode PAD and individual SiPMs: The noise of aSiPM is some orders higher than noise of a single PMT anode PAD,creating some constrains for the circuits connected to the matrixoutputs, and it is more relevant in those detector configurations thatproduce output signals close to the intrinsic noise of the SiPMs.

We reviewed all the available readout networks for MODs, and testedthese for the specific case of the detector block conformed by SiPMAscoupled to continuous scintillator crystal. The results were not goodand we concluded that those readout networks are not suitable for thisnew type of detector block.

The noise in electronic systems is usually treated with filteringcircuitry. These can be passive filters or active filters that also canbe classified as high pass, band pass, low pass and notch filters,according to the frequency attenuation shape produced. The passive onesare designed to produce amplitude reduction of the noisy signals, butthese produce some amplitude reduction in the useful signal too. On thecontrary, the use of active filters avoids the amplitude reduction inthe useful signal and produces better signal to noise ratio. A typicalsingle stage active filter includes a passive component (i.e. capacitor,resistor, . . . ) at the negative input of an operational amplifier(OpAmp) and another passive component (i.e. resistor, capacitor, . . . )in the feedback loop of the OpAmp. If we want to actively filter adefined quantity of signals, we normally require the same number ofactive filters, while each active filter requires an OpAmp with itsbiasing circuitry, a feedback loop passive component and a passivecomponent at input. These different active filters will have their owndifferent outputs, so that, if it is necessary to add a group of them, afurther additional circuit is required.

Although MODs have an uncountable number of outputs, in the presentinvention we will show a filtering and adding circuit that permits tofilter all the MOD outputs in a similar way as described above, doingthe active filtering and the adding process in a single stage thatfurthermore shares the same OpAmp for a group of noisy input signals. Inthis way it is possible to use a limited number of OpAmps, quite lowcompared to the number of processed MOD outputs.

In U.S. Pat. No. 6,747,263, Popov describes a simple network thatmaintains isolated each matrix output while extracts its signalssimultaneously, to its corresponding row and column outputs of the wholecircuit. This circuit suits very well the PSPMTs functionality due tothe very low noise of the PSPMTs anode outputs, which remain low, evenafter mixing all these in the Popov readout network. Trying to use thePopov network in the new MODs, (the SiPMAs) fails due to the fact thatat the end of the rows and columns a lot of noisy signals are addedgenerating a bad signal to noise response in all rows and columns,worsening too much the energy and spatial resolutions among otherfeatures of the detector, when compared to a system that processes allmatrix outputs individually.

In. US2013/0293296 A1, Proffit proposes a network based on diodes inplace of the resistors previously used by Popov with the aim to overcomethe noise issues. The diodes have a threshold voltage and it isnecessary to overcome it before any signal could travel through thediode, so, this threshold will takes account of the noise, while realsignals are high enough to rise over threshold and reach the networkoutput after crossing the diodes.

The problem with Proffit network comes from the diodes behavior. As thediodes will subtract their own thresholds to any signal crossing them,the proportion of signals reduced at the output will be higher if thesignals are close to the threshold voltage, but will be negligible ifthe signals are very high compared to threshold, which is characteristicof the Proffit network, limiting and conditioning its usability.

This type of high level signals can be normally obtained in SiPMAconnected to scintillator arrays (made of stacked small pixelatedscintillator crystals). When a gamma ray reaches one pixel (among allwhich are stacked inside the scintillator array), although the lightemitted flows everywhere, a lot of photons will go to the side where isattached the SiPMA, but will flow through the single SiPM that is facingthe touched crystal (or a very limited quantity of SiPMs in front ofthat crystal), producing high level signals.

Although, scintillator arrays connected to matrix detectors, eitherPSPMTs or SiPMAs, are very common, there is a different configurationusing a monolithic single (or continuous) crystal connected to thosementioned matrix detectors. This configuration gives exceptionalpossibilities to determine the Depth Of Interaction of gamma ray in thedetector, which is a very important advantage in some applicationsdemanding very high spatial resolution [Christoph], disregarding thatthe planar resolution is not limited by any pixel size of a crystalarray.

The use of continuous crystal coupled to SiPMAs configuration producessome special features in the output signals that is important to takecare of, when extracting these signals by any means, including a readoutnetwork.

Following the previous description about light travelling in thepixelated crystals, when a gamma ray reaches the monolithic scintillatorcrystal, again the light emitted flows everywhere, again a lot ofphotons will go to the side where the SiPMA is attached, but in thiscase the light will flow through the monolithic crystal reaching all (oralmost all) the SiPMs that are distributed along the side of themonolithic scintillator, and sharing the photons among all of them, thusproducing a relatively low level signal, compared with the hypotheticsignal produced by the same gamma ray reaching a pixelated crystal,although all the signals together, in the configuration with monolithiccrystal, make up the equivalent signal for that gamma ray in aconfiguration with a pixelated crystal.

Some research groups are very active developing the SiPMA technology andattempting to validate different detector configurations, includingPopov's, Proffit's networks among others. [A. González. et al.“Simulation Study of Resistor Networks Applied to an Array of 256SiPMs”. Nuclear Science, IEEE Transactions on (Vol: 60, Issue: 2)].

When the SiPMs are arranged in a SiPMA configuration, similar to thoseof the PSPMT, the designers are tempted to use the same previous readoutconfigurations to extract and process the output signals, but this doesnot work properly due to the fact that SiPMs are too noisy devices [A.González et al.: Performance study of a Wide-Area SIPM ARRAY, ASICSControlled. IEEE Transactions on Nuclear Science, Vol. 62, Issue: 1], Anew readout network to solve these limitations is needed.

Trying to use the networks described by Siegel or Popov fails in generalwhen using SiPMAs because those networks add or mix all the matrixsignals, adding the whole noise and worsening the signal to noise ratio.This is even worse if we use the continuous monolithic crystal plusSiPMA configuration, because with the gamma ray energy distributedacross all the SiPMs inside the SiPMA, the individual output signals ofthe SiPMs are close to noise level and the output signal cannot bedistinguished from noise.

The use of Proffit's network solves part of the described problems. Inthe configurations using SiPMAs plus Pixelated Scintillator Crystals,the gain of the SiPMs can be adjusted so that the noise at all SiPMs canbe below diodes threshold, thus enabling signal triggering just whenreal signals arrive and allowing correct processing of these, althoughall outputs are affected with distortions in a different way each.

On the contrary, when we try to use the Proffit's network in a detectorconfiguration including a continuous crystal plus a SiPMA, it fails in asimilar way that Popov's network. As the signals are shared among allSiPMs in the SiPMA, these are very close to the noise level, and thusare too affected by the diode threshold voltage cut, making verydifficult (when not impossible) to process these and obtaining usabledata. In this way, a lot of SiPMs elements will lead to null signals,instead to the real values, and the remainders SiPM elements will leadto signals which are reduced in relevant percentages, disregarding thatare different percentages for each SiPM output signal.

In the present invention, we filter all the matrix device output signalsinstead of cutting everything that could be lower than certainthreshold, solving the problems cited in the above paragraph regardingthe Proffit's network. Furthermore, our invention improves signal tonoise ratio on each matrix device output signal compared to the Popov'snetwork, which collects all signals as well as all noises, worsening thepossibilities of extracting useful information from the reduced numberof outputs of this network.

The filtering capability of the proposed readout network topology, at avery early stage of the signal processing, increases the signal to noiseratio, preserving the useful part of the signal, while reducing theintrinsic noise of the individual SiPMs, before mixing these in the nextstages of processing, solving the issues related to noise when usingSiPMs and SiPMAs.

When working with matrix signals arriving from SiPMAs coupled tomonolithic crystals configurations, the filtered network proposed by thepresent invention has better performance than the known ones, such asthose proposed by Proffit, because both, real signal and noise, cannotbe distinguished by their amplitudes, when signal amplitudes are closeto noise, such as the case of detector blocks including monolithicscintillator crystals. However, according to the present invention theycan always be weel characterized by means of their respectivefrequencies, without taking into account their amplitudes.

These and other objects, advantages, and features of the invention willbecome apparent to those skilled in the art from the detaileddescription and the accompanying drawings. It should be understood,however, that the detailed description and accompanying drawings, whileindicating preferred embodiments of the present invention, are given byway of illustration and not of limitation. Many changes andmodifications may be made within the scope of the present inventionwithout departing from the spirit thereof, and the invention includesall such modifications.

BRIEF DESCRIPTION OF THE INVENTION

In order to appropriately deal with the noisy SiPMA output signals, wepropose a readout network topology for a Matrix Output Device with anumber of outputs given by the cross combination of “m” rows and “n”columns, labeled as Source(i, j), wherein “i” ranges 1 to m and “j”ranges 1 to n, that comprises a basic filtering block, replicated forall the matrix outputs, and separately assigned to each one; eachfiltering block containing a pair of filtering circuits having a commoninput connection to its assigned matrix output and providing twoseparate, symmetrical and filtered outputs labeled Col. (j) and Row(i);all the Row(i) outputs incoming from the same row “i”, but differentcolumns are connected together to the low impedance input of anamplifier linked to the “i” row, that completes the active filtering andmixing topology of the whole path, giving the corresponding AmpRow(i)output, and all the Column(j) outputs incoming from the same column “j”,but different rows, are connected together to the low impedance input ofan amplifier linked to the “j” column, that completes the activefiltering and mixing topology of the whole path, giving thecorresponding AmpCol(j) output; the complete topology of the readoutnetwork appears revealed expanding “i” and “j” to their respectiveranges.

According to particular embodiments of the readout network topology thefiltering block is made of a pair of CR Filtering Circuits.

According to additional particular embodiments of the readout networktopology the filtering block is made of a pair of CL Filtering Circuits.

According to additional particular embodiments the different commonoutputs of the Filtering blocks, for rows, Row(i), and for columns,Column(j), are connected to amplifier circuits of the types “of charge”or “of current”, with low input impedance, compared with the impedanceof the Filtering circuit, being at least 10 times lower.

According to additional particular embodiments the different commonoutputs of the filtering blocks, for rows, Row(i), and for columns,Column(j), are connected to the negative inputs of the amplifiercircuits and a resistor is used in the feedback loop between OpAmpoutput and its negative input.

According to additional particular embodiments the totality of thedifferent common outputs of the Filtering blocks, for rows, Row(i), andfor columns, Column(j), represents the totality of outputs of thedetector to be digitized.

According to additional particular embodiments the different Amplifieroutputs for rows, AmpRow(i) and for columns, AmpCol(j), represent theoutputs of the detector to be digitized.

According to additional particular embodiments a first resistor chaininterconnects the outputs of all rows AmpRow(i) and a second resistorchain interconnects the outputs of all columns, AmpCol(j); the ends ofthe resistor chains enable to extract directly, on real time, the “x”and “y” position by means of the COG algorithm. An adding circuit can beprovided to add the signals obtained at the different interconnectionpoints of the resistor chain for rows, AmpRow(i) and for columns,AmpCol(j), which represents the second momentum and is a function of theDOI, inside the continuous crystal coupled to the matrix output device.

The present invention also refers to a matrix output devicecharacterized in that it comprises the readout network topology definedabove. According to particular embodiments, the device comprising thereadout network topology defined, is selected from among SiPMA, PSPMTsand APDs arrays.

According to additional particular embodiments the matrix output deviceis selected from SiPMA, PSPMTs and APD arrays. An adding circuit can beprovided to add the signals obtained at the different interconnectionpoints of the resistor chain for the rows, AmpRow(i) and for thecolumns, AmpCol(j), which represents the second momentum and is afunction of the DOI, inside the continuous crystal coupled to the matrixoutput device.

According to additional particular embodiments the matrix output deviceis coupled to continuous monolithic scintillator crystals, or pixelatedscintillators. An adding circuit can be provided to add the signalsobtained at the different interconnection points of the resistor chainfor rows, AmpRow(i) and for columns, AmpCol(j), which represents thesecond momentum and is a function of the DOI, inside the continuouscrystal coupled to the matrix output device.

According to a preferred embodiment of the device comprising the readoutnetwork, the matrix output device is coupled to continuous monolithicscintillator crystals, preferably the MOD, is a SiPMA which is coupledto a monolithic crystal.

The present invention also refers to detector block (which can be aX-ray detector or a gamma ray detector characterized in that itcomprises a matrix output device comprising the readout network topologydefined above.

According to particular embodiments the detector block comprises amatrix output device that is selected from among a SiPMA, PSPMTs and APDarrays.

According to additional particular embodiments of the detector block,the matrix output device is coupled to a monolithic continuescintillation crystal or pixelated scintillation crystal.

According to preferred particular embodiments of the detector block, thematrix output device is a SiPMA and is coupled to a monolithic continuecrystal.

The present invention also refers to the use of the readout networktopology previously defined or to the use of a device previouslydefined, or to the use of the detector block defined above, in a processfor obtaining images generated by X-ray sources or gamma ray sources.

According to particular embodiments the invention refers to the use ofthe readout network topology defined or the use of the device previouslydefined, wherein the device comprises a Silicon Photomultiplier matrixdevices connected to monolithic scintillator crystals or to pixelatedscintillator crystals.

BRIEF DESCRIPTION OF THE DRAWING(S)

Various exemplary embodiments of the subject matter disclosed herein areillustrated in the accompanying drawings in which like referencenumerals represent like parts throughout, and in which:

In the figures “GND” means a ground connection.

FIG. 1 is a schematic of the pinout of a generally known Matrix OutputDevice with “m” rows and “n” columns;

FIG. 2A shows an example of a PSPMT, with 8 Rows×8 Columns, representinga standard Matrix Output Devices (MOD);

FIG. 2B shows an example of a SiPMA with 16 Rows×16 Columns,representing a standard Matrix Output Devices (MOD);

FIG. 3A shows a typical biasing circuit for a SiPM;

FIG. 3B shows a typical biasing circuit for a SiPM;

FIG. 4A is a circuit with the typical topology (state of the art) of anactive filter, including passive components connected from input,Source(i, j) to the negative input of the Operational Amplifier (OpAmp),labeled as AmplifierA, and a feedback passive component connected fromOpAmp output to the negative input of the OpAmp;

FIG. 4B is an example of using a single OpAmp for mixing the multipleinput signals (Source(i, l) . . . Source(i, n)), without interferencewith each other, and actively filtering of these input signals,producing a single amplified output for each row, AmpRow(i). Thefunctioning of this circuit is similar to that described in FIG. 4A, butthe passive components at the left part from the labeled “Middle pointof the active filter” are distributed along all the matrix, thus we willdivide this circuit for the description as conformed by two parts: theLeft Part of the Active Filter, corresponding to what we called theFiltering circuits, and the Right Part of the Active Filter,corresponding to the circuitry of the OpAmp, AmplifierA, with itsfeedback loop resistor R_feedbac;

FIG. 4C is an example of using a single OpAmp for mixing the multipleinput signals (Source(l, j) . . . Source(m, j)), without interferencewith each other, and actively filtering of these input signals,producing a single amplified output for each column, AmpCol(j). Thiscircuit is divided in two parts in a similar way that FIG. 4B;

FIG. 4D is a simplified diagram of the right side of the circuit in FIG.4C;

FIG. 4E is a simplified diagram of the right side of the circuit in FIG.4B;

FIG. 5A is a block diagram of the filtering block, which is used as abasic building block of the readout network topology made of a pair offiltering circuits (constituting the left part of the active filters),that provide outputs divided in Rows and Columns to the subsequentamplification stage and Right Part of the active filters;

FIG. 5B is an exemplary filtering blocks, using a pair of filteringcircuits with the configuration of a capacitor in series with aresistor;

FIG. 5C is an exemplary filtering blocks, using a pair of filteringcircuits with the configuration of a capacitor in series with aninductor;

FIG. 6 is the general block diagram of the proposed filtering readoutnetwork topology of the present invention;

FIG. 7 is the schematic diagram of a proposed filtering readout networkusing a pair of CR filtering circuits to conform the filtering block;

FIG. 8 is the schematic diagram of a proposed filtering readout networkusing a pair of CL filtering circuits to conform the filtering block;

FIG. 9 is the schematic diagram of a proposed filtering readout networkusing a pair of CR filtering circuits to conform the filtering block,further comprising resistor chains at Columns and Rows terminals toapply the COG algorithm and reduce the output number from Row+Columns toonly 4 signals;

FIG. 10 is the schematic diagram of a proposed filtering readout networkusing a pair of CL filtering circuits to conform the filtering block,further comprising resistor chains at Columns and Rows terminals toapply the COG algorithm and reduce the output number from Row+Columns toonly 4 signals;

FIG. 11 is the schematic diagram of a proposed filtering readout networkusing a pair of CR filtering circuits to conform the filtering block,further comprising two resistor chains at Columns and Rows terminals;the first resistor chain to apply the COG algorithm and reduce theoutput number from Row+Columns to only 4 signals, and the secondresistor chain to obtain a variable dependent on the Depth ofInteraction (DOI) given by an additional signal; and

FIG. 12 is the schematic diagram of a proposed filtering readout networkusing a pair of CL filtering circuits to conform the filtering block,further comprising two resistor chains at Columns and Rows terminals;the first resistor chain to apply the COG algorithm and reduce theoutput number from Row+Columns to only 4 signals, and the secondresistor chain to obtain a variable dependent on the Depth ofInteraction (DOI) given by an additional signal.

In the figures, the initials or legends appearing therein, mean thefollowing:

R=Row;

C=Column;

F=Filter output;

S=Source;

R_f=R_feedback;

Ro=R out;

AR=Amplifier Row;

AC=Amplifier Column); and

DOI=Depth of Interaction.

In describing the preferred embodiments of the invention which areillustrated in the drawings, specific terminology will be resorted tofor the sake of clarity. However, it is not intended that the inventionbe limited to the specific terms so selected and it is understood thateach specific term includes all technical equivalents which operate in asimilar manner to accomplish a similar purpose. For example, the word“connected,” “attached,” or terms similar thereto are often used. Theyare not limited to direct connection but include connection throughother elements where such connection is recognized as being equivalentby those skilled in the art.

DETAILED DESCRIPTION OF THE INVENTION Glossary

MOD: It is the acronym of Matrix Output Device and has the sameconventional meaning as in the state of the art.

Filtering circuit: It is here a minimum circuit block with one inputconnection and one output connection, which may be selected from twomodels, the first model including a capacitor in series with a resistorand the second model including a capacitor in series with an inductor.

Filtering block: It is a basic building block of the readout networktopology and its realizations. It is made of a pair of similar filteringcircuits, one used to generate an output signal to be processed ascontainer of row information and the other used to generate an outputsignal to be processed as container of column information.

Readout network topology: It is a generic block diagram of an electronicnetwork, which could generate multiples specific circuitry realizationswith a similar functioning.

Detector and detector block are expressions indistinctly used, and referto the radiation detector block, which can be an X-ray detector or agamma ray detector.

After reviewing all available readout network for Matrix Output Devices(MODs) and testing them, a new readout network topology is provided,specifically to overcome the issues related to the high noise level ofthe SiPMs, which appropriately operate with the requirements of adetector block conformed by a monolithic scintillator crystal plus aSiPMA. Of course, this new readout network topology (that can generatevarious readout network configurations) can work fine too (and better),with the MODs that are not as restrictive as SiPMAs. Each descriptionand each embodiment of the present invention regarding SiPMA is assumedto be applicable in general to any MOD.

In order to appropriately deal with the noisy SiPMA output signals, inthe present invention we propose a generic filtered readout networktopology for Matrix Output Devices characterized by the spread of areplicated basic filtering block along the outputs of the whole matrix,each filtering block containing a pair of filtering circuits connectedto each SiPM output by a common input connection, providing twoseparate, symmetrical and filtered outputs—one each filtering block—.These filtered outputs are further grouped by columns and rows to belater injected into amplifier circuit inputs to obtain actively filteredand amplified output signals, good enough to reproduce the planar impactposition of the gamma ray in a monolithic crystal and the DOI ifrequired.

Regarding FIG. 1, it represents the schematic of the pinout of a generalMatrix Output Device (MOD) with “m” rows and “n” columns, which is thetarget for the solution given by the present invention. The matrixoutputs are current sources, thus, these were labeled accordingly andenumerated in the typical matrix form as Source(i, j), where “i” rangesfrom 1 to “m” and “j” ranges from 1 to “n”. “m” is the number of rowsand “n” is the number of columns.

FIG. 2A is a PSPMT with 8 rows and 8 columns (64 outputs), while FIG. 2Bis a SiPMA with 16 rows and 16 columns (256 outputs). Both are examplesof matrix output devices and have output sets as shown in FIG. 1, whichmay benefit from the present invention in order to reduce the number ofelectronic channels required to reproduce the coordinates of the gammarays detected at the scintillators coupled to these MODs.

Each matrix element of the SiPMA is a SiPM that requires its own biasingas can be seen in FIG. 3A and FIG. 3B. The SiPM element Dij has a symbolof diode. It is biased in reversed polarity from Vcc across a limitingresistor Rp(ij). The capacitor Cp(i j), holds sufficient charge toprovide the output current when the SiPM opens after a nuclear eventappears. The output labeled as Source(i, j) in the circuit of FIG. 3Arequires a low impedance current mode connection, while the same outputin the circuit of FIG. 3B requires voltage mode connection, because thislatter one includes the resistor Rg(ij), which drains the SiPM current,producing a voltage source instead of a current.

Our goal is to provide a readout network to deal with the uncountableMODs outputs (labeled in the form Source(i, j) in FIG. 1, where “i”ranges from 1 to “m” and “j” ranges from 1 to “n”, being “m” the numberof rows and “n” the number of columns) and be able to reproduce theoriginal coordinates of the impact in the scintillator, and doing iteven for very noisy devices such as SiPMA.

In the present invention we use extensively, by simplicity, the conceptof SiPMA as a specific example of a MOD, but in all cases it should beunderstood that it is applicable in general to any type of MOD.

A good way to filter the uncountable SiPMA outputs could be to includeactive filtering at any output, Source(i, j), but this normally willinvolve the use of a replicable circuit (as the one in FIG. 4A) with thesame number of OpAmps (m×n), which increases the circuit space, andpower requirements, disregarding the cost. Furthermore, the number offiltered outputs is the same as the number of inputs (m×n), in such away that, if we want to reduce them, we should include a further readoutnetwork (such as Popov, etc). That is why, an alternative circuit isproposed instead of replicating the circuit of FIG. 4A, for all the MODoutputs Source(i, j).

As it is known in the state of the art, a signal number reduction torows plus columns is possible if appropriate mixing of signals isapplied avoiding mutual interferences. To do that, we need to add thefiltered signals of common rows on one side (FIG. 4B) and common columnson the other side (FIG. 4C). Taking advantage of the low impedance ofthe negative input of the OpAmp (labeled AmplifierA in both circuits) inan active filter configuration; we noted that it is possible to do theadding process (avoiding interferences with each other) at the middlepoint of the active filter, using a single OpAmp to actively filter allthe signals incoming from various Left part filters that share theOpAmp, by means of injecting their currents together into the lowimpedance negative input of the OpAmp (FIG. 4B and FIG. 4C), thatfurthermore will add the currents of all the incoming signals. Thiscircuit shares the OpAmp labeled as AmplifierA, and the passivecomponent at the feedback loop of the OpAmp, labeled as R_feedback,while includes separate passive components in the input side (Ci1 r, Ci2r, . . . , Cinr in FIG. 4B and C1 jc, C2 jc, . . . , Cmjc in FIG. 4C),receiving all the separate noisy signals (Source(i,l), to Source(i,n) inFIG. 4B and Source(l,j), to Source(m,j) in FIG. 4C) and injecting theircurrents together (added) in the negative input of the single OpAmplabeled as AmplifierA in both cases.

As explained, this functionality of the circuit makes it to look like ifseparate active filters were connected to each MOD output, therefore, inthe descriptions below we will assume the existence of filters connectedbetween each MOD output and the specific amplified rows: AmpRow(i) inFIG. 4B, and amplified columns: AmpCol(j) in FIG. 4C, withoutdistinguishing that these are sharing part of the circuit.

After the assumption of the preceding paragraph and by simplicity, inthe explanation of the subsequent drawings we will suppress the biasingand feedback loop components in the OpAmp circuits, in such a way thatthe right side of the circuits of FIG. 4B and FIG. 4C, from the labeled“middle point of the active filter”, will be respectively replaced bythe diagrams of FIG. 4E and FIG. 4D. At the same time, every circuitline of passive components horizontally deployed at the left part of thecircuits of FIG. 4B and FIG. 4C, from the labeled “middle point of theactive filter”, will be named as “filtering circuit” in the descriptionbelow. Furthermore, this filtering circuit may be of the type (CijrRijror CijcRijc) shown in FIG. 5B or (CijrLijr or CijcLijc) shown in FIG.5C, and thus represented as generic boxes—Fijc, Fijr in FIG. 5A—too.

In the present invention, we propose a generic filtered readout networktopology for Matrix Output Devices, composed by the spread of a basic“filtering block” along the outputs of the whole matrix, workingtogether with a set of amplifier circuits that meet the following:

1. If the size of the MOD matrix is “m” rows and “n” columns, (m×n),such as that which pinout is shown in FIG. 1, then we can conform thewhole readout network by the spread of the filtering block along thematrix outputs Source(i, j), provided that the variable “i” ranges from1 to “m”, while “j” ranges from 1 to “n”. FIG. 6 represents the diagramof a general embodiment of the proposed readout network.

2. The filtering block contains a pair of filtering circuits (FIG. 5A),connectable to any MOD output by the common input connection that can beseen at the top left corner, labeled as Source(i, j), extracting twoseparate, symmetrical and filtered outputs labeled as Col. (j) at thetop right corner, and Row(i) at the bottom left corner.

3. As can be seen on FIG. 6, the number “n” of different output signalsgenerated by the same number of filtering circuits for rows (Fijr),labeled as Row(i), are connected together and later injected into thelow impedance input of the amplifiers, similar to the one in FIG. 4E,(the Right part of the active filter in FIG. 4B) and represented at theright side of the diagram in FIG. 6, where the corresponding amplifiedand filtered output signals are labeled as AmpRow(i).

4. In a similar way of previous point 3, (speaking of FIG. 6) the number“m” of different output signals generated by the same number offiltering circuits for columns (Fijc), labeled as Column(j), areconnected together and later injected into the low impedance input ofthe amplifiers, similar to the one in FIG. 4D, (the right part of theactive filter in FIG. 4C) and represented at the bottom side of thediagram in FIG. 6, where the corresponding amplified and filtered outputsignals are labeled as AmpCol.(j).

5. What we consider “the readout network outputs” in FIG. 6, are theamplified outputs related to all Rows and Columns of the matrix, beingRows+Columns equal to the output channel number of the readout network.These outputs are located at the bottom and right sides of theschematics in FIG. 6, as well as in FIG. 7 and FIG. 8, and are labeledas AmpRow(i) and AmpCol.(j).

6. An appropriated acquisition and digitizing electronics for the “m+n”channels is required and specific software to process all digitizedsignals and provide planar positioning of the detected rays (gamma or X)and DOI, if required.

As a result of the functioning of the described readout network in FIG.6, the filtering circuits working together with the OpAmp circuitsconform an equivalent “active filter network” with the ability toattenuate the noisy signals reaching the readout network inputs from theMOD outputs Source(i, j), while the real signals from nuclear events arepassed through the circuitry without attenuation and are symmetricallydirected only to its specific “Row(i) output” and its specific“Column(j) output”, without interfering with each other and furtheramplified to generate the corresponding amplified and filtered signalsAmpRow(i) and AmpCol.(j).

The more simple and effective filtering circuits to conform thefiltering block mentioned in the previous general description are the CRfilter presented in FIG. 5B and the CL filter presented in FIG. 5C. Suchcombinations reduce the offset variation caused by temperaturevariations and noise coming from electronics. In all the previousdescriptions, the diagram of FIG. 5A can be replaced by the circuitsshown in FIG. 5B and FIG. 5C. In this way we will describe specificembodiments of the present invention.

In the preferred embodiment, the filtering circuit is composed by aCapacitor in series with a Resistor, to conform the filtering blockshown in FIG. 5B. It is easy to obtain the new circuit from FIG. 6, byreplacing the general filtering block (as FIG. 5A), attached to eachSource(i, j), by the specific “CR based” filtering circuit of FIG. 5B.The result is the schematic of the FIG. 7. The signals from a specificMOD output, Source (i, j) are symmetrically divided in two componentsthat will not interfere with each other, neither with any other arrivingsignal from a different MOD output. One of the two components is treatedby the “High Pass filter” created by the passive components Cijc, Rijcand R_Feedback and the Amplifier with output AmpCol(j), (see FIG. 4Ctoo). The cutting frequency of the filter is given by the parameterCijc×R_Feedback, although the maximum gain is limited by the ratioR_Feedback/Rijc, to increase the circuit stability. The other one of thetwo components is treated by the “High Pass filter” created by thepassive components Cijr, Rijr and R_Feedback and the Amplifier withoutput AmpRow(i), (see FIG. 4B too). The cutting frequency of the filteris given by the parameter Cijr×R_Feedback, although the maximum gain islimited by the ratio R_Feedback/Rijr, to increase the circuit stability.

In an alternative embodiment, the filtering circuit is composed by aCapacitor in series with an Inductor, to conform the filtering blockshown in FIG. 5C. It is easy to obtain the new circuit from FIG. 6, byreplacing the general filtering block (as FIG. 5A), attached to eachSource(i, j), by the specific “CL based” filtering circuit of FIG. 5C.The result is the schematic of the FIG. 8. The signals from a specificMOD output, Source (i, j) are symmetrically divided in two componentsthat will not interfere with each other, neither with any other arrivingsignal from a different MOD output. One of the two signal components istreated by the “Band Pass filter” created by the passive componentsCijc, Lijc and R_Feedback and the Amplifier with output AmpCol(j). Thecentral frequency of the filter is given by the parameter Cijc×Lijc.Fortunately, Lijc has the parasitic resistance R(Lijc) which limits themaximum gain to the ratio R_Feedback/R(Lijc), to increase the circuitstability. The other one of the two signal component is treated by the“Band Pass filter” created by the passive components Cijr, Lijr andR_Feedback and the Amplifier with output AmpRow(i). The center frequencyof the filter is given by the parameter Cijr×Lijr. And the maximum gainis limited by the ratio R_Feedback/R(Lijr), increasing the circuitstability. Being R(Lijr) the parasitic resistance of the inductor Lijr.

In the preferred embodiment of the present invention, the SiPMA (or MODin general) is optically coupled to a monolithic scintillator crystal.The readout network inputs (Source(i, j) (using the circuit of FIG. 7),“i” ranges 1 to m; “j” ranges 1 to n) are connected to the matrixoutputs of the SiPMA (as seen in FIG. 1 also labeled as (Source(i, j)),and the two types of filtering circuit component outputs (divided inrows and columns) are connected to the low impedance inputs of theamplifiers that complete the active filtering functionality of thenetwork. The amplified signals, labeled as AmpRow(i) and AmpCol. (j); (iranges 1 to m and “j” ranges 1 to n) reach a number equal to the sum ofcolumns and rows, and can be later processed analogically or digitallyto obtain the planar impact position of the gamma ray in the monolithicscintillator crystal and the DOI if required. In this preferredembodiment, what we consider “the network outputs” are the amplifiersoutputs related to all Rows and Columns of the matrix, beingRows+Columns equal to the output channel number of the readout network.These outputs are located at the bottom and right sides of the schematicin FIG. 7, and labeled as AmpRow(i) and AmpCol.(j).

An alternative embodiment can be obtained from a previous preferredembodiment by replacing the circuit of FIG. 7 by the circuit of FIG. 8.The SiPMA is optically coupled to a monolithic scintillator crystal. Thereadout network inputs (Source(i, j) (using the circuit of FIG. 8), “i”ranges 1 to m; “j” ranges 1 to n) are connected to the matrix outputs ofthe SiPMA (as seen in FIG. 1 also labeled as (Source(i, j)), and the twotypes of filtering circuit component outputs (divided in rows andcolumns) are connected to the low impedance inputs of the amplifiersthat complete the active filtering functionality of the network. Theamplified signals, labeled as AmpRow(i) and AmpCol.(j); (i ranges 1 to mand “j” ranges 1 to n) reach a number equal to the sum of columns androws), and can be later processed analogically or digitally to obtainthe planar impact position of the gamma ray in the monolithic crystaland the DOI if required. The network outputs are located here too at thebottom and right sides of the schematic in FIG. 8, and labeled asAmpRow(i) and AmpCol.(j).

In both cases, preferred or alternative embodiments, an appropriatedacquisition and digitizing electronics for the “m+n” channels isrequired and specific software to process all signals and provide planarpositioning of the detected ray (gamma or X) and DOI if required.

In alternative embodiments (FIG. 9 and FIG. 10), starting with theprevious preferred and alternative embodiments of FIG. 7 and FIG. 8; andbased on the previous art (i. e. Popov), the amplified signals(AmpRow(i) and AmpCol. (j)) can be connected to a pair of dividerresistor chains (one for Rows, shown at right side, and the other forColumns, shown at bottom side) to reduce the output quantity to 4 and beable to apply the COG algorithm. The resistor chain established tocalculate X coordinate, located at bottom side, is labeled R0 x, R1 x,R2 x, . . . , Rnx, and the outputs at its edges are labeled “X−” and“X+”. In a similar way, the resistor chain established to calculate Ycoordinate, located at right side, is labeled R0 y, R1 y, R2 y, . . . ,Rmy, and the outputs at its edges are labeled “Y−” and “Y+”.

The value for X position can be calculated as X=(X+)−(X−)/((X+)+(X−))and the value for “y” position can be calculated asY=(Y+)−(Y−)/((Y+)+(Y−)).

Assuming that a continuous scintillator crystal is coupled to the SiPMA,the gamma rays impinging the scintillator will produce a distribution oflight over the SiPMA, activating a lot of SiPMs each time, which allowsobtaining, not only the planar coordinates where the gamma ray reachesthe scintillator, but also the DOI of the gamma ray inside thescintillator. This task can be done on real time, applying the analogprocessing described by [Christoph] and digitizing just one signalrepresenting the DOI, or can be accomplished reading and digitizing theindividuals signals of every row and column and determining the lightshape and its corresponding DOI.

In alternative configurations (FIG. 11 and FIG. 12), starting with theprevious two alternative embodiments of FIG. 9 and FIG. 10; and based onthe previous art (i.e. Christoph), a further pair of resistor chains(one for Rows, shown at right side, and the other for Columns, shown atbottom side) can be connected by the input side to the nodes of bothprevious resistor chains (tied to all AmpRows(i) and AmpCol. (j)outputs) and can be connected by the output side to an electronic addingcircuit (labeled AmpB) that makes up all the voltages at those nodes toobtain analogically an additional signal representing DOI and labeled asDOI Signal.

In this latter configuration only 5 signals are digitized to provide thegamma ray three-dimensional impact positioning. (X+, X−, Y+, Y−, and DOISignal).

It should be understood that the invention is not limited in itsapplication to the details of construction and arrangements of thecomponents set forth herein. The invention is capable of otherembodiments and of being practiced or carried out in various ways.Variations and modifications of the foregoing are within the scope ofthe present invention. It also being understood that the inventiondisclosed and defined herein extends to all alternative combinations oftwo or more of the individual features mentioned or evident from thetext and/or drawings. All of these different combinations constitutevarious alternative aspects of the present invention. The embodimentsdescribed herein explain the best modes known for practicing theinvention and will enable others skilled in the art to utilize theinvention.

We claim:
 1. A readout network topology for a Matrix Output Device witha plurality of matrix outputs given by the cross combination of “m” rowsand “n” columns, labeled as Source(i, j), wherein “i” ranges 1 to m and“j” ranges 1 to n, the readout network topology comprising a basicfrequency filtering block, replicated for each of the matrix outputs,and separately assigned to each matrix output; wherein: each frequencyfiltering block includes a pair of filtering circuits having a commoninput connection to its assigned matrix output and providing twoseparate, symmetrical and filtered outputs labeled Col. (j) and Row(i);all the Row(i) outputs incoming from the same row “i”, but differentcolumns are connected together to the low impedance input of anamplifier linked to the “i” row, that completes the active filtering andthe mixing topology of the whole path, giving rise to the correspondingAmpRow(i) output; and all the Column(j) outputs incoming from the samecolumn “j”, but different rows, are connected together to the lowimpedance input of an amplifier linked to the “j” column, that completesthe frequency active filtering and the mixing topology of the wholepath, giving rise to the corresponding AmpCol(j) output.
 2. The readoutnetwork topology according to claim 0, wherein the frequency filteringblock is made of a pair of CR Filtering Circuits.
 3. The Readout Networktopology according to claim 0, wherein the frequency filtering block ismade of a pair of CL Filtering Circuits.
 4. The readout network topologyaccording to claim 0, wherein the different common outputs of theFiltering blocks, for rows, Row(i), and for columns, Column(j), areconnected to amplifier circuits of the types “of charge” or “ofcurrent”, with low input impedance, compared with the impedance of theFiltering circuit, being at least 10 times lower.
 5. The readout networktopology according to claim 0, wherein the different common outputs ofthe filtering blocks, for rows, Row(i), and for columns, Column(j), areconnected to the negative inputs of the amplifier circuits and aresistor is used in the feedback loop between OpAmp output and itsnegative input.
 6. The readout network topology according to claim 1,wherein the totality of the different common outputs of the Filteringblocks, for rows, Row(i), and for columns, Column(j), represents thetotality of outputs of the detector to be digitized.
 7. The readoutnetwork topology according to claim 1 wherein the different Amplifieroutputs for rows, AmpRow(i) and for columns, AmpCol(j), represent theoutputs of the detector to be digitized.
 8. The readout network topologyaccording to claim 0 wherein a first resistor chain interconnects theoutputs of all rows AmpRow(i) and a second resistor chain interconnectsthe outputs of all columns, AmpCol(j); the ends of the resistor chainsenable to extract directly, on real time, the “x” and “y” position bymeans of positioning advanced algorithms.
 9. The readout networktopology of claim 0 wherein the matrix output device is selected from aSiPMA matrix.
 10. The readout network topology of claim 0, wherein thematrix output device is coupled to continuous monolithic scintillatorcrystals, or pixelated scintillators.
 11. The readout network topologyaccording to claim 0 wherein an adding circuit is provided to add thesignals obtained at the different interconnection points of the resistorchain for rows, AmpRow(i) and for columns, AmpCol(j), the values ofwhich are used to obtained the DOI, inside the continuous crystalcoupled to the matrix output device.
 12. A matrix output devicecomprising the readout network topology with a plurality of matrixoutputs given by the cross combination of “m” rows and “n” columns,labeled as Source(i, j), wherein “i” ranges 1 to m and “j” ranges 1 ton, the readout network topology comprising a basic frequency filteringblock, replicated for each of the matrix outputs, and separatelyassigned to each matrix output; wherein: each frequency filtering blockincludes a pair of filtering circuits having a common input connectionto its assigned matrix output and providing two separate, symmetricaland filtered outputs labeled Col. (j) and Row(i); all the Row(i) outputsincoming from the same row “i”, but different columns are connectedtogether to the low impedance input of an amplifier linked to the “i”row, that completes the active filtering and the mixing topology of thewhole path, giving rise to the corresponding AmpRow(i) output; and allthe Column(j) outputs incoming from the same column “j”, but differentrows, are connected together to the low impedance input of an amplifierlinked to the “j” column, that completes the frequency active filteringand the mixing topology of the whole path, giving rise to thecorresponding AmpCol(j) output.
 13. The matrix output device accordingto claim 12 selected from a SiPMA matrix.
 14. The matrix output deviceaccording to claim 12 that it is coupled to continue monolithicscintillation crystals.
 15. The matrix output device according to claim13 that is a SiPMA that is coupled to a monolithic crystal.
 16. Adetector block characterized in that it comprises a matrix outputdevice, which comprises a readout network topology with a plurality ofmatrix outputs given by the cross combination of “m” rows and “n”columns, labeled as Source(i, j), wherein “i” ranges 1 to m and “j”ranges 1 to n, the readout network topology comprising a basic frequencyfiltering block, replicated for each of the matrix outputs, andseparately assigned to each matrix output; wherein: each frequencyfiltering block includes a pair of filtering circuits having a commoninput connection to its assigned matrix output and providing twoseparate, symmetrical and filtered outputs labeled Col. (j) and Row(i);all the Row(i) outputs incoming from the same row “i”, but differentcolumns are connected together to the low impedance input of anamplifier linked to the “i” row, that completes the active filtering andthe mixing topology of the whole path, giving rise to the correspondingAmpRow(i) output; and all the Column(j) outputs incoming from the samecolumn “j”, but different rows, are connected together to the lowimpedance input of an amplifier linked to the “j” column, that completesthe frequency active filtering and the mixing topology of the wholepath, giving rise to the corresponding AmpCol(j) output.
 17. Thedetector block according to claim 16, wherein the matrix output deviceis selected from a SiPMA.
 18. The detector block according to claim 16,wherein the matrix output device is coupled to a continue monolithicscintillation crystal or a pixelated scintillation crystal.
 19. Thedetector block according to claim 18, wherein the matrix output deviceis a SiPMA and is coupled to a continue monolithic crystal.
 20. Aprocess for obtaining images generated by X-ray sources or gamma raysources comprising detecting the X-ray or gamma ray, and processing thesignal obtained by means of a readout network topology with a pluralityof matrix outputs given by the cross combination of “m” rows and “n”columns, labeled as Source(i, j), wherein “i” ranges 1 to m and “j”ranges 1 to n, the readout network topology comprising a basic frequencyfiltering block, replicated for each of the matrix outputs, andseparately assigned to each matrix output; wherein: each frequencyfiltering block includes a pair of filtering circuits having a commoninput connection to its assigned matrix output and providing twoseparate, symmetrical and filtered outputs labeled Col. (j) and Row(i);all the Row(i) outputs incoming from the same row “i”, but differentcolumns are connected together to the low impedance input of anamplifier linked to the “i” row, that completes the active filtering andthe mixing topology of the whole path, giving rise to the correspondingAmpRow(i) output; and all the Column(j) outputs incoming from the samecolumn “j”, but different rows, are connected together to the lowimpedance input of an amplifier linked to the “j” column, that completesthe frequency active filtering and the mixing topology of the wholepath, giving rise to the corresponding AmpCol(j) output.
 21. The processof claim 20, wherein the readout network topology is included in amatrix our device.
 22. The process of claim 20, wherein the matrix ourdevice is comprised in a detector block.